Secret communicating system



Aug. 20, 1929. Q 1 wE s JR ,725,032

SECRET COMMUNICATING SYSTEM Filed July 6, 1927 3 Sheets-Sheet 1 By W ,4 ORA/E) 1929- I c. 1.. WEIS, JR 1,725,032

SECRET COMMUNICATING SYSTEM Filed y 192 a Sheets-Sheet 2 61 ,3; 400950 awn-5550A 4 5; 950 1500 awe-a5 5 \1 v I 500-6050 7 3 8000 3550 6' fiaZ. g 5

/N-l/ENTO/-? CHARLES L I'VE/.5 JR.

g- 1929- c. L. WEIS. JR 1,725,032

SECRET COMMUNICATING SYSTEM Filed July 6, 1927 3 Sheets-Sheet 3 47 Q4 7600m0R8950'u 5 o 2 //v vs/v TOR 671A BL 55 L W475 JR.

il atenteel Aug. 26, E929.

sir

CHAR-LES L. WEIS, JR., OF BROOKLYN, NEW YORK, ASSIGNOR T BELL TELEPHONE LABORATORIES, INCORPORATED, OF NEW YORK, N. Y., .A CORPORATION OF NEW YonKi.

SECRET COMMUNICATING SYSTEM.

Application filed July 6, 1927.

This invention relates to transmission systems and more particularly to the method of and means for providing secrecy in the transmission of messages over such systems.

The basic principle of this invention is disclosed in Patent No. 1,573,924 to H. Fletcher, February 23, 1926, and the invention is a modification of the secrecy system disclosed in this patent. It is in brief, a system in which the normally transmitted frequency band is divided into a number of sub-bands which are then reorganized either by relocating the positions of the sub-bands or by inverting the frequencies Within cerlain sub-bands, or both into the original frequency band spectrum for further transmission. As shown in the Fletcher patent, a multiplicity of combinations are possible possessinc varying degrees of secrecy which may be shirted at periodic intervals to provide a system. which has a high degree of secrecy. In the invention to be described herein, the method used in shifting, relocating and inverting the sub-bands is by modulation or demodulation and the method of segregation is by the use of band filters as described in the above mentioned patent disclosure.

1* is an object of this invention to increase the secrecy of the system referred to above increasing the number of possible sei'et combinations and to facilitate the shift- 7 g from one combination to a different combination.

I mother object is to simplify the means for confusing the sub-bands and reorganizing them.

A further object is to improve the efficiency transmission through a secrecy system such disclosed in the above mentioned patent and to simplify two-Way transmission "irough such a system.

The advantages of this invention. will be sought out in the detailed description of accompanying drawings in which:

i 1 is :1 schematic drawing of a radio transmission terminal showing the method of arranging the secrecy circuit for two-Way operation li i s. 2 and 3 are schematic drawings of the secrecy circuit itself, Fig. 3 being the key itching arrangement for confusing or the sub-bands after being resame frequency is Y and then recombining them; and

Serial No. 203,703.

Fig. 4 is a chart of a complementary key arrangement.

The secrecy circuit to be disclosed herein is essentially a one-way device and when used in a complete transmission channel or two- Way circuit, it becomes necessary either to employ two identical secrecy circuits or provide for transmission in either direction by transferring a single secrecy circuit from one line to the other. In the present system only one secrecy circuit is used. an arrangement of voice-operated relays being provided to shift the circuit from the receiving line to the transmitting line. The shifting is performed by short-cireuiting the input and output of the line not in service the time of shift being controlled by the direction of the signals. lVhilc the invention is applicable to many different types of two-Way circuits, for purposes of illustration, it is here shown applied to a radio telephone circuit such as a transoceanic system.

In. Fig. l is shown schen'iatically the necessary terminal apparatus for such a two-Way radio system to properly control transmission through the secrecy circuit. In the normal condition as shown, relays ll), 11, 12. 13 and 14 are so arranged that the incoming line through the terminal apparatus is open to incoming signals While the transmission line is short circuited. The signal received on the antenna system B will pass to the hybrid coil 18 with its balancing network N since relay is not energized and the incoming line is open. The signal then passes from the hybrid coil 18 through the secrecy circuit. the operation of which will be explained later, '11 the direction of the arrow and into repeaters Rep and Rep The output of repeater Rep is short circuited by the armature of relay 12 preventing the incoming signal from reaching the transmitting system T. The output of repeater liep however is not short circuited by the armature of relay 11 and it reaches a. delay circuit D and a rectifier Rec simultaneously. The delay circuit be of any suitable type such as described in the C. Mathes application Serial No. 747,164, filed November 1, 1924. The signal from the delay circuit then passes through hybrid coil 19 and into the outgoing line L to receiving lines such as subscriber lOO which case the output circuit of the coil is short circuited by the armature of relay 14: in the output of the rectifier .olec The delay circuit D delays the signal sufficiently to allow relay l 'l to short circuit the line before the signal reaches it. This is the action of certain non-singing circuits well known in the art.

In transmitting, the signal comes into the hybrid coil 19 over line L, and leaves over line 20 in the direction shown by the arrow, arriving at a rectifier Rec and a delay circuit D simultaneously. The rectifier Rec and delay circuit D are similar to rectifier Ree and delay circuit D respectively. The line 20 is not short circuited by relay 14; except when signals being received so it is nor mally open and the signals to be transn'iittcd reach the rectifier liiec and the delay circuit D The outgoing 11118 21, however, is not normally open for transmission, it being short circuited by relays 12 and 13 in their normal position. To maize this line operative, these relays are actuated by the output of rectifier r Rec signal being delayed suliiciently by delay circuit ED to allow the short circuits to be removed. The output of this rectifier also actnates relays 10 and 11, putting short circuits on both sides of the secrecy "circuit in the receiving path. The path of the signal to be transmitted is now into hybrid coil 18, through the secrecy circuit in the direction of the arrow and through repeaters Rep and Rep The output of repeater Rep is new short circuited, however, by relay 11, but the output of repeater Rep may pass into the transmitting system T. Any transmitted signals picked up by the receiving apparatus R from the transmitter 'II will not reach the hybrid coil 18- since relay 10 is energized and a short circuit exists on the incoming line.

The operation of the terminal apparatus just described causes both the incoming and the outgoing signals to pass tl'irouggh the secrecy circuit in the same direction while short circuits exist on the input and output of the secrecy circuiton either line when the other is operative.

Figs. 2 and 3, taken together, show in detail the circuit schematic of the portion of Fig. l. designated as the secrecy circuit. With the secrecy circuit removed from the system, the signals from the hybrid coil pass on. line L through the armatures of relay 25, through network :26 which is designed to have a loss equal to that of the secrecy circuit, through armatures of relay 2? to l1ne L which may terminate at repeaters itep and RePT shown in F g. 1. When relays and 27 are actuated, the upper armatures of: relay 25 connect line L, to line 30, line 30 terminatingtat transformer 31, the input of the' secrecy circuit, while the armatures of relay 2'? connect line lb to line 32, line v32 being the termination of the secrecv circuit. in

case any difficulty arises in the functioning of the secrecy circuit apparatus, the network 26 may be substituted therefor Without interference to straightforward transmission. When the network is being used and the secrecy circuit not functioning, armature of relay connects ground to line 29 and lamp 40 through battery 11 for alarm purposes. With the upper contact of key 422 closed, a bell is put in parallel with lamp 40 for the same purpose. The lower Contact of key 12 controls the substitution of the network 26. v

The input to the secrecy system is a vacuum tube 3% having high resistance in series with its grid. This arrangement is employed a voltage limiting device to protect later apparatus.

The output of the Voltage limiter is connected through the transformer 36 to band filters F F F F and compensating filter CF These band filters are of the type disclosed in the Campbell Patent 1,227,113, May 22, 1917, and the compensating filter, of the type disclosed in the Mills Patent 1,616,193, February 1, 1927, which serves to improve the cut-oil characteristics of filters F F at the extreme limits of the signal band. The band filters divide a signal band and as in this case the speech band, into four equal "frequency ranges or sub-bands, namely,

Mill-950, 950-1500, 1500-2050 and 2050-2600 cycles. lghe total range is from 400 to 2600 covering the important speech frequencies.

Each sub-band now has an individual channel to be known as the A, B, C and channels or sub-bands for purposes of description. Each channel has a modulator associated with filters 1 1,1 E and F of the type disclosed in the Carson Patent 1,343,300., June 15, 1020, designated as M M M and M in the drawings. These are balanced modulators which eliminate the oscillator frequency from the outgoing line. The modulators are supplied by Hartley type oscillators 0 OB, U and G of 7600, 6500 and 5950 cycle frequencies, respectively. Modulation with these particular frequencies reduces all the sub-bands to the same frequency level if only the proper frequency products of modulation are selected. This is accomplished by four filters F,.;, with the same frequency discrimination, in the outputs of the four" modulators, maintaining the four distinct channels. In this manner, sucband A of 400-950 cycles modulated with 7600 cycles becomes a band of 8000-8550 cycles selected by filter F in channel A. club-band B of 950-1500 cycles modulated with 7050 cycles becomesa band of the same frequency range and selected by filter in channel it? and so on for channels C and D.

The outputs of the four filters F are confaected to the armatures oil sixteen relays, four for each channel, designated as AA, Ali,

for channel A, BA to BD for channel B and so on for channels 0 and D, the operation of which will be described later.

The outputs of the key circuits terminate in the four channels mentioned above in which are four demodulators or mmlulators D D D and D These demodulators are similar to the modulators M M M and M as shown by the detailed circuit of demodulator D These demodulators are supplied with frequencies from oscillators O' 0'3, 0' and O of the Hartley type. By varying the tuning of the oscillators, each oscillator furnishes two modulating frequencies. Oscillator O supplies demoluator D with frequencies of 7600 cycles or 8950 cycles; while oscillator O supplies demodulator D with frequencies of 7050 or 9500 cycles, oscillator O furnishes demodulator D with frequencies of 6500 or 10,500 cycles, and oscillator O furnishes demodulator D with frequencies of 5050 or 10.000 cycles. Just what frequency is supplied by each oscillator is determined by the operation of relays B R R and R associated therewith, and which are controlled by the preceding switches.

The outputs of the demodulators D D D and D connect to band filters F F F F' and compensating filter Cit- These band filters are similar to the band filters F F F and F respectively, and COIHPQIh satin; filter CF is similar to compensating filter CF, and is for the same purpose. The hand filters are selective to the same frequein cies as filters F F F and F respectively, the combination of their outputs having the same overall range as the input speech band. The outputs of the band filters are connected in parallel to line 32, which passes the band onto the outgoing line L, through the armatures of relay 2?.

Returning now to the key circuits proper, what occurs when certain keys are operated will now be described to explain the operation. of the circuit and to show the ability of this arrangement to procure every possible combination of frequency sub-lmnds in a simplemanner. A simplification over prior ar 'angements is obtained by reducing all the sub-bands to the same frequency level which in this instance is 80008550 cycles.

The lettering on the key relays and the toys themselves designates their function with respect to the particular channels they control. For instance. the first letter of the markings designates the channels entering the key circuits, while the second letter of the markings shows to which channels or demodulators the bands are going, while the prime letters indicate that the. hand is'inverted in frequency.

For example, with the contacts of key 42 closed, and keys AA, BB, CG and DD operated, relays AA, BB, CC, DD are actuated through individual circuits and relays 25 and 27 are actuated by a. circuit traceable through ground, battery l4, windings of relays 27- and 25, lower armatures of relays AA, BB, CC and DD in succession, and lower contact of key42 to ground. The operation of relays 25 and 27 puts the secrecy circuit in the transmission system. The circuit of lamp 40 is broken at armature 28 and a signal registered to show that the secrecy circuit is in the system. It will be observed that the operation of four relays in the four channels is necessary to form a combination, that is one relay to each channel, sutficcs to cause the actuation of-relays 25 and 27 through the lower armature circuits of the lettered relays although the failure of any relay allows the system to operate through the network.

lVith the keys above mentioned closed, filter F in the A channel is connected to demodulator D through the upper armature of relay AA. conductor 46, primary of transformer 47 and conductor 48. This band of 8000-8550 cycles is demodula ted with a frequency of 7600 cycles and the lower sideband selected by filter F' which is 400050 cycles, bringing the sub-band back to its original frequency lev l. A similar circuitmay be traced connecting filter F of channel B to demodulator D as follows, through upper arn'iature of relay BB, conductor 50, demodulator D and conductor 48. For filter F of channel C, the'circuit is through upper armature of relay CC, conductor 51, demodulator D and conductor 48, and for filter F of channel it is through the upper armature of relay DD, conductor 52, demodulator D and conductor 48. The frequencies in channels B. l and D are demodulated by frequencies of 7050. 6500, and 5950 cycles, respectively, reducing sub-bands B, C and D of 9501500, 15002050 and 2050-2600 respectively to their original frequency positions. The lettering of the keys used, that is, Alt, BB, CC and DD denotes this con'ibination, the lettters pointing out that each band remains in its own channel and is not inverted.

In the foregoing: paragraph, the circuits of one combination of four keys has been traced. All the possible circuits for one particular sulrband will now be described and what is true of this sub-band applies to the others. Choosing channel A, which, like the other channels. has a frequency band of 80008550 cycles at filter F the effect of closing key AA has just been traced. lVhen" key AA is closed, the same circuit is completed to the dcmmlulator D by the lcft hand contact of the key as by key AA, while the right-hand contact closes a circuit through conductor 55, windings of relay 1 and battery 56. thus actuating relay R and causing the oscillator O, to supply a frequency of 8950 cycles to the demodulator. The lower sideband of the demodulation frequencies is procured, therefore, with a frequency range of from 400-950 cycles and which Will pass filter F.,. The frequencies, however, which passed through filter F are now inverted, that is, the portion of the signal at 400 cycles now lies at 950 cycles.

lVhen key AB is closed, relay AB connects channel A to demodulator D or channel. B through the upper armature of relay AB, conductor 57-, demodulator D and conductor 48. This connection demodulates the 8000-8550 band with 7050 cycles providing a sidcband of 950-1500 cycles or the frequency range of channel B. of channel A are now relocated in channel 13. Key AB places the band of channel A of 400-950 cycles in channel l3 and inverts it by energizing relay R through conductor 58, winding of the relay and battery 59, causing oscillator O' to furnish a frequency of 9500 cycles. Demodulating a band of 8000-8550 cycles with a frequency of 9500 cycles gives the inverted sideband of 1500-950, which will pass filter F Key AG connects channel A to demodulator D through upper armature of. relay AC, conductor 61, demodulator D and conductor 48, modulates the frequency band 8000 to 8550 cycles with a frequency of 6500 cycles thereby shifting the 400-950 band to the 1500-2050 frequency range or C channel. Key AC, through conductor 62, causes the oscillator O' to furnish a frequency of 10,050, the lower side band of which inverts and shifts the 400-950 cycle sub-band. to the C channel range as a band of 2050 to 1500 cycles.

Keys Al) and Al)" perform the same function with respect to channels A B through conductors 63 and 6% respectively.

Taking another combination of four keys, for example, AC, Bl), CA and DB, We have a secret combination the circuits in brief of which are as follows. Key AC connects channel A to demodulator D through. the upper armature of relay AC, conductor 6]. and conductor 48, stepping up the 400-950 cycle range to the 1500-2050 range. Key BD connects channel B to the demodulator D modulating With a frequency of 10,600 cycles through the upper armature of relay Bl), conductor 68 and conductor 48 for the channel and conductor 69 for the oscillator OD, stepping up the 950-1500 band to the 2050-2600 range and inverting it. Key CA connects channel C to demodulator D through the upper armature of relay CA, conductor '21 and conductor 48 stepping the 1500-2500 frequencyfband to the 400-950.-

range by modulating, it. with 7600 cycles. Lastly, key DB connects channel D to demodulator D at 9500'cycles through the armature of relay DB, conducto1 72 and con- T has, the frequencies cycle mes es ductor 48 for the channel and conductor 73 for the oscillator.

In the forming of combinations, it is seen that there may be three channels in normal order While the fourth is inverted. This combination will not have as high a degree of secrecy as certain other combinations, such as the one just traced. This difierence in degree of secrecy is ably discussed in the Fletcher patent above mentioned.

It is possible, With the circuit justde scribed, however, to invert a sub-band in its own frequency channel and to obtain all possible combinations with, consequently, a large number of secret combinations. It is also possible to invert the Whole signal band by the closing of keys AD, BC, GB and DA. The apparatus shown in Fig. 3, can, therefore, shift any sub-band from its normal channel to any other channel and invert it in that channel. The closing of the four keys may be done in one operation making practical a rapid change from one combination to another.

Referring to Fig. l, two charts are shown, one to be used. at each terminal of the transmission line. These charts show the manner of decoding or unscrambling a message from a sending station which has been scrambled in accordance with the system described herein. These charts are complementary in position of lreys that is, key AB is located on one chart in the same position as key BA on the other chart, hey BB is located on one in the same position as key BB on the other, etc, meaning that if key AB is closed at the transmitting station, the pressing of key BA in the same position at the receiving station ill return channel A to its proper position. in the frequency spectrum. For example,

the closing of key All takes sulrband A of 400-950 cycles, relocates it in the 13 channel inverted, and the closing of lie BA. takes the inverted signal of the B channel to the A channel and reinverts it to return it to its normal position. In practice, the positions on these charts may be designated. by numbers to increase the transmission of code combinations.

The frequencies of the four sub-bands, namely, 400-950, 950-1500, 1500-2050 and 2050-2600, cover a total range of 400-2600 To simplify the method of scrambling these bands are modulated With frequencies of 7600, 7050, 6500 and 5950 cycles to reduce them all to a band 550 cycles wide ranging from 8000 to 8550 cycles. The choosing of these particular frequencies means that all higher order products of the ,modulation of a carrier frequency and any associated voice frequency up to and includ- .ing the fifth order product are eliminated by the filters from further transmission except in the instance of the carrier plus twice the Voice frequency, of which a. very small amount is present in the 400950 cycle range.

This invention has been disclosed as embodied in a certain specific arrangement, but it is capable of embodiment in many other types of circuits without departing from the spirit of the invention as defined by the claims.

What is claimed is:

1. In a signaling system, a plurality of means for dividing the signaling band into a, corresponding number of sub-bands of different frequency ranges, means for shifting the frequency positions of said sub-bands, and for, alternatively, transmitting certain or all of said sub-bands while maintaining them in their frequency positions with respect to one another, a plurality of circuits each selective of a different sub-band, and means intermediate said first means and said circuits for inverting the frequency order within the selected sub-bands.

2. In a signaling system, a plurality of means for dividing the signaling band into a corresponding number of sub-bands of different frequency ranges, frequency shifting and switching means for producing in an outgoing circuit from the incoming sub-bands every possible complete combination producible by shifting the frequency positions of said sub-bands with and without frequency inversions of individual sub-bands and by inverting the frequencies Without shifting the frequency level of a sub-band as a whole.

3. In a signaling system, a plurality of means for sub-dividing signaling components into a number of fragmentary portions on a frequency basis, means to reduce all portions to a common frequency level in a series of separate circuits, a corresponding series of circuits each selective of a different portion of the frequenc range of said signaling components, SLi( last mentioned circuits including means for shifting the individual portions of the signaling components from the common frequency level to the respective frequency ranges of which said circuits are individually selective, an outgoing circuit common to said last mentioned series of circuits, and switching means positioned between said two series of circuits for variously and individually interconnecting respective circuits of one series with those of the other to alter the frequency positions of the signaling portions in the outgoing cir- 'cuit. V

4. In a signaling system, means for dividing the signaling band into a plurality of subliands, modulators to reduce all of said subbands to the same frequency level, second stage modulators to return said sub-bands to their original range of frequencies in said aling band, and switching means intermeuiate said first and second stage modus for inverting the frequencies within any of said sub-bands and interchanging any of said sub-bands with each other to form any one of all possible combinations of interchanges and inversions.

5. In a signaling system, an incoming line and an outgoing line, means connected to said incoming line for dividing the signaling band into a plurality of frequency ranges, modulators individual to each of said frequency ranges for reducing each to a common frequency level, means for maintaining each of said ranges in individual channels, a plurality of secondary modulators, means connected to the outputs of said secondary modulators for combining said plurality of frequency ranges into said signaling band for transmission to said outgoing line, and means intermediate said secondary modulators and said second means for connecting any of said channels to any of said secondary modulators and for interchanging and inverting the frequency or-' der of any of said ranges.

6. In a signaling system, an incoming line and an outgoing line, means connected to said incoming line for dividing the signaling band into a corresponding number of sub-bands, means individual to each of'said sub-bands for reducing each to the same range of frequency components, means for converting said respective sub-bands of the same frequency components into sub-bands having the same total range as said signaling band for transmission to said outgoing line, and means for impressing any of said sub-bands of the same frequency components on said modulating means in any sequence and combination.

7 A frequency changing system for a band of frequency components comprising a filter and modulator for shifting the band to a new frequency level and selecting one sideband only of a modulated wave, a plurality of second stage modulators, circuit connections for selectively impressing the resulting sideband in the first modulator on any one of the second stage modulators, each last mentioned modulator operating at either of two shifting frequencies such that with one of the frequencies operative, a sideband results occupying a predetermined absolute frequency range with the frequency components in their nor mal order, and with the other mentioned shifting frequency operative, a sideband results occupying said predetermined absolute frequency range with the frequency components in the inverse of their normal order, the absolute frequency range of the out ut of each second stage modulator being di erent from the others, and switching means to determine on which of the two shifting frequencies the second stage modulators operate.

8. In a signaling system, an incoming line and an outgoing line, a secrecy circuit intermediate said lines comprising a plurality of means for dividing a signaling band on said incoming line into sub-bands, means for confusing said sub-bands, means for reuniting said sub-bands after confusion and impressmg them on sald outgoing line, a network having a transmission loss substantially equal.

and an outgoing line, a secrecy circuit intermediate said line comprising a plurality of means for dividing a signaling band on said incoming line into sub-bands, a series of relay circuits for confusing said sub-bands certain of which are operated as combinations, means for reuniting said sub-bands after confusion and impressing them on said outgoing line, a network having a transmission loss substantially equal to that of said secrecy circuit, and a second series of relay circuits associated with said first series for controlling the substitution of said network upon the incomplete operation of any one of a combination of said first mentioned series of relay circuits.

10. In a secrecy signaling system, a plu-.

rality of filters for dividing a signaling band of the order of 400 to 2600 cycles per second into sub-bands of frequencies extending from 400 to 950, 950 to 1500, 1500 to 2050, and 2050 to 2600 cycles per second, modulators for reducing said sub-bands to four bands each extending from 8000 to 8550 cycles, demodulators for shifting said 8000 to 8550 cycle bands to occupy said original transmission band of frequency limits of the order of 400 to 2600 cycles per second, and switching means intermediate said modulators and demodulators for interchangeably impressing said 8000 to 8550 cycle bands on said demodulators in different orders for varying the order of occurrence of the resulting sub-bands in said transmission band.

11. In a secrecy signaling system, a plurality'of filters for dividing asignaling band into a plurality of'sub-bands, modulators each having a difierent modulating frequency individual to said filters, means inthe output circuits of said modulators all selective to a side-band occupying the same range of frequencies, resulting from the modulation in said modulators, the modulating frequencies being so related to the frequencies of the sub bands and of the side bands selected after modulation that substantially all products of modulation except those falling in the individual selected sideband are eliminated, demodulators for shifting said sidebands of the same frequency range to. the same and other positions in the original signaling band, and switching means intermediate said selective means and said demodulators for impressing any of said sidebands on any of said demodulators in any combination.

In Witness whereof, I hereunto subscribe my name this th day of June A. D., 1927.

CHARLES L. JR;- 

